Remove the URI limitation from external markdown links
The Markdown Module of Redmine limits the possible URIs in markdown written links (RedmineTextFormattingMarkdown). But for us it is a very important feature to be able to link directly from Redmine to other apps. Therefore we need to be able to set links e.g. with the URI zpl://... (zeplin.io App on MacOS). With Textile this is possible, but not with Markdown.
IMHO the security gain of the limitation is small, especially since there is no limitation with Textile.
Remove the URI limitation in Markdown (/lib/redmine/helpers/uri.rb). Alternatively, the possible URIs could be made adjustable.